1. Technical Field
The invention relates to a thermoelectric semiconductor component and to an electronic component containing such a thermoelectric semiconductor component.
2. Discussion of Related Art
Thermoelectric converters and thermoelectric generators are used in many fields of technology, the primarily aim being to utilize heat generated by technically necessary processes. The use of thermoelectric generators is even possible in the production of semiconductor components. The heat that is to be converted into electric energy may result from any number of different factors. The operating energy of integrated circuits, for example, leads to the entire circuit being heated and in the case of conventional microchips can well reach the 70-80° C. range.
This heating is generally undesired, so special precautions need to be taken in the components in order to prevent thermal damage to specific electronic elements. The heat may be dissipated in a conventional manner, or specific layers, series of layers, or materials may be designed and deployed beforehand, in the circuit design stage, in such a way, with regard to their thermal conductivity, that sufficient dissipation of any heat produced during operation is ensured. In devices such as mobile telephones, utilizing the significant amounts of heat produced by the high-frequency components used therein could extend the duration of use within a single battery charging cycle. If any temperature differences arise, a thermoelectric generator may even replace the conventional battery in low-consumption devices.
Such converters may also be used for cooling. Conventional cooling devices can be supported in this way. Converters designed as Peltier coolers are particularly advantageous, however, where conventional methods of dissipating operating heat cannot be applied due to miniaturization of components.
The suitability of semiconductor materials for use in thermoelectric semiconductor components such as Seebeck or Peltier elements is generally described by a dimensionless figure of merit ZT, which is proportional to the square of the Seebeck coefficient S and to the temperature, and inversely proportional to the specific electrical resistance ρ and the thermal conductivity κ. The figure of merit ZT is defined as follows:ZT=S2·T/ρ·κ
Thermoelectric materials that are widely used commercially, such as bismuth telluride (Bi2Te3), have a figure of merit ZT of approximately 1, whereas silicon, as a bulk material, has a figure of merit ZT of approximately 0.01. The latter is due to the silicon having a high thermal conductivity, which counters the formation of a temperature gradient in a piece of silicon material.
It has recently been shown that when silicon nanowires (silicon materials with structure sizes in the nanometer range) are used, ZT values of 0.6 or even 0.4 are possible at room temperature; A. I. Boukai et al. “Si-Nanowires as efficient thermoelectric materials”, Nature 451, 168 (2008); A. I. Hochbaum et al. “Enhanced thermoelectric performance of rough Si nanowires”, Nature Vol. 451, 163 (2008). Boukai et al. used rectangular wires with structure sizes in the 10-20 nm range, and Hochbaum et al. used wires with sizes in the 20-300 nm range that had rough surfaces and circular cross-sections. The observed increase of almost two orders of magnitude in the ZT value for silicon, i.e., from 10−2 to values of approximately 1, is mainly attributed to a strong reduction in thermal conductivity inside the silicon nanowires. This effect, known as “phonon drag” is dependent of the size and shape of the nanowires and on obstacles which limit heat flow, such as surface roughness of the wires.
It would be desirable to translate these findings into technologically useful devices.
Hence, the technical problem addressed by the present invention is that of providing a thermoelectric semiconductor component which has improved properties compared to thermoelectric semiconductor components whose manner of operation is based on the properties of bulk semiconductor material.